Apparatus for preparing snow surface and method for controlling a hydraulic circulation between such an apparatus and a tractor

ABSTRACT

The invention relates to an apparatus for snow surface preparation for attachment to a tractor, comprising a vibration plate and a hydraulically driven exciter device for driving the vibration plate, with the exciter device being connectable to a working hydraulic system of the tractor and being driven by the same in such a way that a closed hydraulic circulation is produced between exciter device and working hydraulic system. In order to reduce the risk of overload of the exciter device, a control device is provided which monitors at least one operating parameter of the hydraulic circulation and functionally disconnects the exciter device from the working hydraulic system depending on a predetermined limit value for the at least one operating parameter. The invention further relates to a method for controlling a hydraulic circulation between a working hydraulic system of a tractor and a hydraulically driven exciter device for a vibration plate of an apparatus for preparing the snow surface which can be attached to the tractor.

The invention relates to an apparatus for preparing the snow surface for attachment to a tractor, comprising a vibration plate and a hydraulically driven exciter device for driving the vibration plate, with the exciter device being connectable to a working hydraulic system of the tractor and being driven by the same in such a way that a closed hydraulic circulation is produced between exciter device and working hydraulic system. The invention further relates to a method for controlling a hydraulic circulation between a working hydraulic system of a tractor and a hydraulically driven exciter device for a vibration plate of an apparatus for preparing the snow surface which can be attached to the tractor.

Apparatuses for preparing snow surfaces, which are also known as snow compactors, are used in preparing snow surfaces, especially for winter sports. In this connection, this also means the preparation of the respective snow surfaces, with the same being smoothed and compacted. The term snow surfaces shall primarily mean (ski) pistes, but also cross-country skiing tracks, ski jumps and freestyle installations such as half-pipes and fun parks.

The most common embodiment of such an apparatus for preparing snow surfaces concerns a rotary snow plough pulled by a tractor, especially a snow groomer, with heavy rubber, plastic or steel plates which are attached thereto and partly have several members. In the case of these apparatuses for preparing snow surfaces, lumps of snow and ice situated on the snow surface to be prepared are cut into small pieces by the rotary snow plough and are smoothed and compacted by the action of the weight of the plates pulled over the snow surface. Since these plates rest on the snow and compress the pertinent snow surfaces only by their weight, static compaction is concerned.

In contrast to these statically compacting apparatuses for preparing snow surfaces, there have recently been apparatuses which act dynamically for preparing snow surfaces and which can be used in addition to or even without rotary snow ploughs. A vibration plate is used in these dynamic apparatuses for preparing snow surfaces. This is a plate which is made to oscillate by an exciter device. As a result of the periodic vibration of the plate, the respective snow surface is compressed especially strongly and is compacted substantially more strongly and evenly than would be the case with the purely statically acting rubber, plastic or steel plates.

The stability under load of a snow surface prepared with a dynamic apparatus for preparing snow surfaces is considerably higher than in conventionally prepared snow surfaces. This increases the comfort for users of the respective snow surface and leads to substantial cost benefits regarding the maintenance of pistes or cross-country skiing tracks, because snow surfaces no longer need to be prepared as often with the same surface quality.

The exciter device which makes the plate vibrate comprises one or several hydraulic or fluid power motors whose output is converted into vibrations of the plate. These hydraulic motors are supplied via the working hydraulic system of the respective tractor to which the apparatus for snow surface preparation is attached. The exciter device is connected to the working hydraulic system in such a way that a closed hydraulic circulation is obtained, which means that hydraulic fluid is pumped by the working hydraulic system into the exciter device for supplying the hydraulic motors and flows from the same back again to the working hydraulic system. The passing quantities generated by the working hydraulic system can usually be changed continuously.

If the tractor is a snow groomer, a rotary snow plough is usually operated with the working hydraulic system. The working hydraulic system can provide substantially higher volume flows or flow rates than is necessary for the operation of the exciter device of the apparatus for snow surface preparation. This may lead to an overload of the exciter apparatus, which may thus be damaged or fail.

The invention is therefore based on the object of providing a dynamic apparatus for snow surface preparation and a method for controlling a hydraulic circulation between a working hydraulic system of a tractor and an exciter device of an apparatus for snow surface preparation by which an overload and thus damage to the exciter system can be avoided.

The solution of this object is achieved with an apparatus for snow surface preparation according to claim 1. Advantageous further developments are described in the subs-claims.

The apparatus for snow surface preparation in accordance with the invention therefore differs from the known compactors in such a way that a control device is provided which monitors at least one operating parameter of the hydraulic circulation and functionally disconnects the exciter device from the working hydraulic system depending on a predetermined limit value for the at least one operating parameter. The basic idea of the invention is monitoring with the control device a parameter relevant for the operation of the hydraulic circulation and predetermining a limit value for said operating parameter and storing the same in the control device. The term operating parameter shall be understood as a physical variable which describes the state of the hydraulic circulation during the operation. Such an operating parameter is appropriately monitored by the control device, which parameter depends on the value of the volume flows provided by the working hydraulic system, so that conclusions can be drawn therefrom concerning a possible overload of the exciter device. Principally, the limit value can be a value range. In this case, the control device will functionally disconnect the exciter device from the working hydraulic system at the moment when the actual value of the operating parameter lies outside of the predetermined value range. Preferably however, a maximum or minimum value is predetermined as a limit value. In this case, the control device will functionally disconnect the exciter device from the working hydraulic system at the moment when the actual value of the operating parameter exceeds or falls below the limit value. The limit value shall appropriately be chosen in such a way that the functional disconnection of the exciter device is made by the control device before the exciter device is in a critical state or is overloaded, so that damage to the exciter device or the apparatus for snow surface preparation is avoided.

The term “functional disconnection” of the exciter device from the working hydraulic system shall be understood in the present connection in such a way that the feed of the hydraulic motors of the exciter device by the working hydraulic system is interrupted. No physical disconnection of the exciter device from the working hydraulic system is principally necessary for this purpose. The exciter device is de facto switched off and stops operation. This prevents that the exciter device is operated with an excessive volume flow, so that damage by overload of the exciter device is avoided.

As soon as a state has been reached which is critical for the exciter device, the existing at least one operating parameter exceeds or falls below the predetermined limit value, the exciter device is functionally disconnected from the working hydraulic system. Preferably, the limit value is dimensioned in such a way that an upward or downward security margin is included, so that reaching a critical state of the exciter device is prevented in any case. The control device therefore acts like an overload protection system which prevents the exciter device from being damaged.

Appropriately, the apparatus for preparing the snow surfaces is arranged in such a way that it can be combined with the largest number of different tractors. The working hydraulic systems of the individual tractors can be arranged in different ways and accordingly their hydraulic pumps can have different maximum volume flows. As a result of the overload protection as granted by the control device it is possible to operate the apparatus in accordance with the invention for preparing snow surfaces with principally all conventional tractors without having to accept any damage or destruction of the apparatus for snow surface preparation or the exciter device due to excessive outputs of the hydraulic pump.

Furthermore, a control potentiometer is usually provided for in the operator stand by means of which the volume flow of the hydraulic pump of the working hydraulic system of the tractor can be set. When an apparatus for snow surface preparation is newly connected to a tractor, it may occur that the control potentiometer is set to a volume flow that is critical for the exciter device of the apparatus for snow surface preparation and the operator forgets to set the volume flow prior to start-up of the apparatus for snow surface preparation to a lower range, i.e. an non-critical range. In the present invention, the control device will immediately disconnect the exciter device after start-up of the working hydraulic system, so that damage to the apparatus for snow surface preparation can be avoided In this situation too.

Advantageously the control device immediately disconnects the exciter device from the working hydraulic system after exceeding or falling below the predetermined limit value. This changeover between the operating states thus occurs directly, without any creeping transition. A creeping transition between the operating states would lead to a considerable heating of the working hydraulic system which is the consequence of losses in the degradation of pressure differences of the hydraulic fluid from the high-pressure to the low-pressure side in the closed circulation. This would lead to considerable damage to the entire hydraulic system. This advantageous embodiment eliminates the likelihood that such damage can occur.

Preferably, the control device is arranged in such a way that the disconnection of the exciter device from the working hydraulic system is achieved in such a way that the control device short-circuits the hydraulic circulation. This means that the control device diverts the flow of hydraulic fluid in such a way that the exciter device is no longer supplied with hydraulic fluid. This preferably occurs in such a way that the control device switches the working hydraulic system to “pressureless circulation”, which means that the hydraulic fluid flow is conveyed without pressure load (or at least at minimal pressure) in the circulation back to the hydraulic fluid tank or back to the pump. The hydraulic circulation is thus also maintained. The exciter device however Is no longer included in the circulation. The short circuit of the hydraulic circulation can principally be carried out both in the apparatus for snow surface preparation as well as in the tractor. IL is advantageous in this respect that by short-circuiting the hydraulic circulation it is not necessary to intervene in the feedback control of the working hydraulic system and the same is thus Independent of the disconnection of the exciter device. The working hydraulic system thus continues to work In an entirely normal fashion In the case of a short circuit. If the control device would disconnect the exciter device In such a way for example that it deactivates the pump completely, the pump might under certain circumstances not immediately be ready for operation again after reactivation.

Appropriately, the control device comprises a sensor for monitoring the at least one operating parameter and further a controllable hydraulic valve for disconnecting the exciter device from the working hydraulic system. The sensor and the hydraulic valve can be arranged as a component or as two separate components. All devices can principally be used as sensors with which the at least one operating parameter can be determined or measured, i.e. it can be determined concretely or with which the at least one operating parameter is monitoring during operation in such a way that any exceeding or falling below the predetermined limit value Is indicated. All hydraulic valves which are principally known from the state of the art and can be used appropriately for the current purpose can be used as hydraulic valves. The hydraulic valve is arranged in such a way that it interrupts the supply of the hydraulic motor of the exciter device by the working hydraulic system upon exceeding or falling below the limit value. Preferably, the hydraulic valve is arranged for short-circuiting the hydraulic circulation or for changing over to pressureless circulation.

In a preferred embodiment of the invention, the sensor and the hydraulic valve are arranged in such a way that the monitoring of the sensor and the disconnection by the hydraulic valve can be performed hydraulically. This means that the sensor and the hydraulic valve both work on a purely hydraulic basis. It is advantageous in this respect that no further systems such as an electric voltage source is required for performing the monitoring and the disconnection. This can be achieved for example in such a way that the hydraulic valve is arranged as a pressure switch valves. It then simultaneously also assumes the function of the sensor. When the set pressure (predetermined limit value) of the hydraulic fluid flow is reached, the valve in the hydraulic circulation releases a pressureless circulation. The switching of the valve can occur for example by a spring-loaded, pressure-controlled sealing cone or the like. The hydraulic valve can principally be subject to outside control. Preferably, it is arranged as a self-controlled component in this variant because thus no additional systems are required for switching and the valve can operate completely autonomously.

It is alternatively preferable that the sensor performs the monitoring and/or the hydraulic valve performs the disconnection in an electric or electromagnetic fashion. In this embodiment, the hydraulic valve and the sensor are preferably arranged as two separate components. It is advantageous in this respect that a precise switching point is ensured. The sensor can be a measuring device for example which monitors the at least one operating parameter, compares It with the preceding limit value and switches the valve upon exceeding or falling below the limit value. The hydraulic valve can be arranged in this embodiment for example as an outside controlled directional control valve which is switched to pressureless circulation upon exceeding or falling below the limit value. The power supply necessary for performing the monitoring and/or disconnection can be arranged either separately in the control device or in the apparatus for snow surface preparation, or the control device can be connected to the power supply of the tractor. It is preferable in both alternatives that the valve switches in an intermittent fashion, which means the switching occurs momentarily and without delay.

Preferably, the hydraulic fluid flow, which means the flow rate of the hydraulic fluid through the hydraulic circulation, is monitored as the at least one operating parameter. This operating is especially suitable for use with the invention. It is principally also possible to use all other operating parameters such as the pressure present in the hydraulic circulation, the flow speed of the hydraulic fluid, the vibration frequency or the speed of the hydraulic motor of the exciter device.

Appropriately, the control device is arranged in the apparatus for snow surface preparation. This simplifies operation because in this way it is not necessary to provide each tractor with a control device. Instead, the control device only has to be built in once into the apparatus for snow surface preparation and the apparatus for snow surface preparation can operate independent of the respective tractor.

In a further preferred embodiment, the control device is arranged to connect the exciter device back to the working hydraulic system after the disconnection of the exciter device as soon as the state of the at least one operating parameter caused by the disconnection is no longer present. If the limit value is predetermined as a maximum value, i.e. the exciter device will be disconnected when the value of the operating parameter exceeds the maximum value, the control device will connect the exciter device back to the working hydraulic system again once the value of the at least one operating parameter is equal again or beneath the maximum value. This is advantageous because the exciter device need not be activated extra again once the at least one operating parameter Is in the noncritical range again. This activation occurs instead automatically.

A further advantage is that an operator can easily find the respective optimal volume flow of the working hydraulic system or the optimal vibration frequency of the exciter device (e.g. 60 Hz). For this purpose, the operator switches on the working hydraulic system with a small volume flow when the apparatus for snow surface preparation is connected. The operator then increases the vibration frequency of the exciter device of the apparatus for snow surface preparation by increasing the throughput of the hydraulic pump of the working hydraulic system by means of the control potentiometer in the operator stand of the tractor. This increase is continued until the exciter device is functionally disconnected by the control device from the working hydraulic system because the at least one operating parameter has exceeded or fallen below the predetermined limit value. After the disconnection, the volume flow of the working hydraulic system is slowly reduced by the operator by means of the control potentiometer again until the control device activates the exciter device again. Once the exciter device is connected again, the volume flow of the working hydraulic system is no longer adjusted again and the exciter device is in the optimal frequency range. If the operator remembers the position of the potentiometer of the working hydraulic system in the optimal frequency range, the apparatus for snow surface preparation can be used directly with the correct vibration frequency when the system is used again with the same tractor.

A display device is preferably provided which indicates the output of the hydraulic pump to the operator of the tractor at which the control device disconnects the exciter device from the working hydraulic system. It is advantageous that in this way the maximum operating point of the hydraulic system is displayed to the operator and it is thus simpler for the operator to set the working hydraulic system in such a way that an optimal operating frequency of the vibration plate is obtained.

The object is further achieved by a method for controlling a hydraulic circulation between a working hydraulic system of a tractor and a hydraulically driven exciter device for a vibration plate of an apparatus for snow surface preparation which can be attached to a tractor, such that at least one operating parameter of the hydraulic circulation is monitored. It is further checked whether the value of the at least one operating parameter exceeds a predetermined maximum value and the exciter device is functionally disconnected from the working hydraulic system once the value of the at least one operating parameter exceeds the predetermined maximum value.

The invention is explained in closer detail by reference to the enclosed drawing, wherein:

FIG. 1 shows a circuit diagram of a hydraulic circulation between an apparatus for snow surface preparation and a tractor.

The only figure shows a hydraulic circuit of the hydraulic circulation 10 of an apparatus for snow surface preparation which is attached to a tractor, The working hydraulic system 11 which is arranged in the tractor comprises a hydraulic pump 13 with two directions of flow in which the displacement volume or output is changeable. The output can be set by means of a control potentiometer (not shown) in the tractor. The pump 13 is connected via lines 18 in the manner with the exciter device 14 that a closed circulation is obtained, which means that feed lines to and discharge lines from the exciter device are present. The exciter device 14 which is arranged in an apparatus for snow surface preparation comprises two hydraulic motors 15 which can be made to oscillate by a vibration plate (not shown) provided in the apparatus for snow surface preparation.

A control device 12 which is arranged as a common control block is interposed between the working hydraulic system 11 and the exciter device 14. The control device 12 is arranged in the apparatus for snow surface preparation like the exciter device 14. The control device 12 comprises a sensor 16 which is arranged as a measuring and switching logic circuit and by means of which the volume flow provided by the pump 13 can be monitored. The sensor 16 measures the volume flow continually and compares the measured value with a stored maximum value. If the measured value is higher than the stored maximum value, the sensor 16 controls a hydraulic valve 17 which is arranged as a cutoff valve. The hydraulic valve 17 is Integrated in the hydraulic circulation 10 and switches the working hydraulic system 11 to pressureless circulation after being triggered by sensor 16. The hydraulic fluid flow conveyed by pump 13 is returned to the pump in a pressureless manner (or at least at minimal pressure) via the hydraulic valve 17. The hydraulic circulation 10 is thus short-circuited and the exciter device 14 is no longer supplied by the working hydraulic system 11, as a result of which the same is cut off.

When the measuring and switching logic circuit 16 determines after changeover to pressureless circulation that the volume flow has fallen beneath the predetermined maximum value, it triggers the hydraulic valve 17 again and the exciter device 14 is switched into the hydraulic circulation 10 again and is thus also driven again. The changeover by the hydraulic valve 17 to pressureless circulation occurs momentarily after the triggering, so that creeping transitions between the two operating states are avoided and thus the resulting negative effects on the hydraulic system are avoided. 

1. An apparatus for snow surface preparation for attachment to a tractor, comprising; a vibration plate; a hydraulically driven exciter device for driving the vibration plate, with the exciter device being connectable to a working hydraulic system of the tractor and being driven by the same in such a way that a closed hydraulic circulation is produced between exciter device and working hydraulic system; and a control device which monitors at least one operating parameter of the hydraulic circulation and functionally disconnects the exciter device from the working hydraulic system depending on a predetermined limit value for the at least one operating parameter.
 2. An apparatus according to claim 1, wherein the control device is configured to disconnect the exciter device from the working hydraulic system directly and without any creeping transition.
 3. An apparatus according to claim 1, wherein the control device is arranged to short-circuit the hydraulic circulation for disconnecting the exciter device from the working hydraulic system.
 4. An apparatus according to claim 1, wherein the control device comprises a sensor for monitoring the at least one operating parameter and a hydraulic valve for disconnecting the exciter device from the working hydraulic system.
 5. An apparatus according to claim 4, characterized in that the monitoring and the disconnection can be performed hydraulically.
 6. An apparatus according to claim 4, wherein the monitoring and/or the coupling can be performed electrically or electromagnetically.
 7. An apparatus according to claim 1, wherein at least one operating parameter is the hydraulic fluid flow of the hydraulic circulation.
 8. An apparatus according to claim 1, wherein the control device is arranged in the device for snow surface preparation.
 9. An apparatus according to claim 1, wherein after the disconnection of the exciter device the control device is configured to re-connect the same again to the working hydraulic system as soon as the state of the at least one operating parameter causing the disconnection is no longer present.
 10. An apparatus according to claim 1, wherein the working hydraulic system comprises an adjustable hydraulic pump and a display device is provided which displays the output of the hydraulic pump at which the control device disconnects the exciter device from the working hydraulic system.
 11. A method for controlling a hydraulic circulation between a working hydraulic system of a tractor and a hydraulically driven exciter device for a vibration plate of an apparatus for snow surface preparation which can be attached to the tractor, comprising the following steps: monitoring at least one operating parameter of the hydraulic circulation; verifying whether the value of the at least one operating parameter exceeds a predetermined maximum value; and functionally disconnecting the exciter device from the working hydraulic system when the value of the at least one operating parameter exceeds the predetermined maximum value.
 12. An apparatus according to claim 2, wherein the control device is arranged to short-circuit the hydraulic circulation for disconnecting the exciter device from the working hydraulic system. 